This invention generally relates to a method and system for monitoring the infusion of parenteral fluids through a fluid delivery system to a patient and, particularly, to the evaluation of the fluid communication between the fluid delivery system and the patient's blood vessel to ensure proper fluid flow.
Fluid delivery systems for infusing parenteral fluids to a patient by means of an infusion pump have enjoyed widespread usage in hospitals. Such systems typically include a bottle of parenteral fluid and an intravenous (IV) set comprising a drip chamber with a piercing element at one end adapted to be inserted through the sealed end of the bottle of parenteral fluid, clear plastic tubing attached to the discharge end of the drip chamber, and means to mount an indwelling cannula on the distal end of the tubing. The cannula mounted at the distal end of the tubing is adapted to be inserted into the patient's blood vessel to thereby deliver parenteral fluid. Roller clamps to manually control fluid flow rates, injection sites, and pressure diaphragms may also be provided with the IV set. The infusion pump is either a piston actuated type pump or a peristaltic type pump wherein a plurality of rollers, cams, or cam-actuated fingers sequentially constrict the flexible plastic tubing of the IV set to drive the parenteral fluid through the tubing.
While these systems have gained widespread acceptance, one common problem with commercially available systems is the difficulty in evaluating the fluid flowing therein in order to detect improper fluid communication between the fluid delivery system and the patient's blood vessels. Generally, if a fluid flow fault develops, the infusion pump will continue to deliver parenteral fluid notwithstanding such fluid flow fault. Thus, for example, if the needle delivering fluid to the patient becomes dislodged from the vein so that the discharge tip of the needle lies in adjacent interstitial tissue, the fluid, which continues to be pumped, infiltrates the interstitial tissue, and may cause serious injury. If the needle becomes completely dislodged from the patient, i.e., an open line, there may be no immediate injury, but the patient does not receive the fluid or drugs needed for treatment. In addition to the above fluid flow faults, other malfunctions of fluid delivery system including air-in-line and occluded tubing or needles.
Detection systems have been developed which sound an alarm or turn off the infusion pump or both when the pressure detected in the parenteral fluid delivery system is greater or less than predetermined maximum and minimum set points. While these control systems have been helpful in some circumstances, they are unable to detect a wide variety of malfunctions in the fluid delivery system. Moreover, these prior systems frequently could not distinguish between fluid flow faults and natural fluid pressure variations within the tubing, and this inability to discriminate resulted in many false alarms.
The method and system described and claimed by Nelson in U.S. Pat. No. 4,534,756 assigned to the present assignee, was a substantial advance in the art of controlling the administration of parenteral fluids to a patient and, particularly, for detecting fluid flow faults in such a system. The method and system described could quickly respond to malfunctions and could distinguish between normal pressure variations and many of the malfunctions normally encountered in the use of such delivery systems.
However, the system of Nelson frequently was not effective in discriminating between fluid flow faults and normal pressure variations at high fluid flow rates. As a result, the need remains for fluid flow fault detection over a wider range of fluid flow conditions particularly at higher fluid flow rates and for better discrimination between normal pressure variations and malfunctions of the delivery system. The present invention satisfies these needs.